Generic finger-tree structure using type families.
A general sequence representation with arbitrary annotations, for use as a base for implementations of various collection types. This is an implementation modified to use associated types instead of functional dependencies.
See the original paper
Ralf Hinze and Ross Paterson, "Finger trees: a simple general-purpose data structure", Journal of Functional Programming 16:2 (2006) pp 197-217. http://www.soi.city.ac.uk/~ross/papers/FingerTree.html
For a tuned sequence type, see Data.Sequence in the containers package, which is a specialization of this structure.
Examples are not available in this package. However I am working on an fingertree-extensible package which will use an idea based on types a la carte to provide composable annotations and that package will include examples :D